The proposed research will concern the course of development of auditory processing in brainstem centers and the susceptibility of the development to changes induced by manipulations of the early sound environment. Rats will serve as experimental subjects, the onset and sequence of unit activity at the VIIIth nerve, cochlear nucleus, and inferior colliculus being observed through acute unit recording and other techniques. Manipulations of the auditory history of individual animals will include deprivations and augmentation of the normally experienced sounds. The objective is to characterize the neural events leading to adult auditory processing and determine their vulnerability to plausible extreme of sound experience.